Method and device for mounting electric component

ABSTRACT

A mounting method and a mounting device are provided, which can mount an electric component with high reliability by using an adhesive. The mounting method includes thermocompression bonding an IC chip onto a wiring board by using an anisotropic conductive adhesive film. During the thermocompression bonding, a top region of the IC chip is pressed against the wiring board with a predetermined pressure, and a side region of the IC chip is pressed with a pressure smaller than the pressure applied to the top region of the IC chip. An elastomer having rubber hardness of 40 or more and 80 or less is used for a compression bonding portion of a thermocompression bonding head. The anisotropic conductive adhesive film contains a binding resin having melting viscosity of 1.0×10 2  mPa·s or more and 1.0×10 5  mPa·s or less.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International ApplicationNo. PCT/JP2004/009726, filed on Jul. 8, 2004, and claims priority toJapanese Patent Application No. 2003-195684 filed in the Japanese PatentOffice on Jul. 11, 2003, the entire contents of which are beingincorporated herein by reference.

BACKGROUND

The present invention relates to a technology for mounting an electriccomponent such as a semiconductor chip on a wiring board. Moreparticularly, the present invention relates to a technology for mountingan electric component by using an adhesive.

In order to directly mount a bare chip on a wiring board such as aprinted wiring board, a method is conventionally known which uses ananisotropic conductive adhesive film in which conductive particles aredispersed in a binder.

In the mounting method using the anisotropic conductive adhesive film,an IC chip is placed on a substrate with the anisotropic conductiveadhesive film bonded thereto, and then the IC chip is pressed and heatedwith a flat bonding head formed of ceramic, metal, or the like, so as tocure the anisotropic conductive adhesive film. In this manner, mountingby thermocompression bonding is performed.

In the method using the bonding head formed of metal or the like forpressurization and heating, there is a problem that a heat applied to afillet portion of the adhesive around the IC chip is insufficient duringthermocompression bonding, thus lowering connection reliability.Moreover, there is also a problem that it is difficult to mount aplurality of IC chips.

Therefore, a technique has been proposed in recent years in order toovercome the above problems, in which thermocompression bonding of an ICchip is performed by using a thermocompression bonding head formed of anelastic material such as silicon rubber.

See, Japanese Patent Laid-Open Publication No. 2000-79611; and JapanesePatent Laid-Open Publication No. 2002-359264.

However, in the aforementioned conventional technique, a pressing forceapplied between a bump and a pattern which connect the IC chip and thesubstrate to each other is not sufficient. Thus, sufficient connectionis not performed and it is not possible to ensure initial conductionresistance and connection reliability after aging.

SUMMARY

It is therefore desirable to provide a mounting method and a mountingdevice, which can mount an electric component with high reliability byusing an adhesive.

In an embodiment, the present invention provides a method for mountingan electric component that includes thermocompression bonding anelectric component onto a wiring board by using an adhesive, whereinduring the thermocompression bonding, a top region of the electriccomponent is pressed against the wiring board with a predeterminedpressure, and a side region of the electric component is pressed with apressure smaller than the pressure applied to the top region.

As used herein, the term “side region” of the “electric component”refers not only to a side of the electric component such as an IC chipbut also to a region around the electric component, such as a portion ofthe adhesive around the electric component.

In an embodiment of the present invention, the electric component isheated at a predetermined temperature and heat the wiring board at atemperature higher than the predetermined temperature during thethermocompression bonding.

In an embodiment of the present invention, a compression bonding portionformed of a predetermined elastomer against a top and a side of theelectric component.

In an embodiment of the present invention, an elastomer is used that hasrubber hardness of 40 or more and 80 or less for the compression bondingportion for the thermocompression bonding.

In an embodiment of the present invention, the adhesive is heated toachieve melting viscosity of 1.0×10² mPa·s or more and 1.0×10⁵ mPa·s orless during the thermocompression bonding.

In an embodiment of the present invention, an anisotropic conductiveadhesive film is used in which conductive particles are dispersed in abinding resin as the adhesive.

In an embodiment of the present invention, the top region and the sideregion of the electric component are simultaneously pressed.

Moreover, the present invention provides in an embodiment a mountingdevice including a thermocompression bonding head having a compressionbonding portion formed of an elastomer having rubber hardness of 40 ormore and 80 or less. The mounting device is arranged to press thecompression bonding portion against an electric component placed on awiring board with a predetermined pressure.

In an embodiment of the present invention, a thickness of thecompression bonding portion of the thermocompression bonding head isequal to or larger than a thickness of the electric component.

In an embodiment of the present invention, a size of the compressionbonding portion of the thermocompression bonding head is larger than anarea of the electric component.

In an embodiment of the present invention, a size of the compressionbonding portion of the thermocompression bonding head is larger than anarea of a region where a plurality of electric components are arranged.

In an embodiment of the present invention, a base for supporting thewiring board is provided, wherein the base includes a heater.

According to the method of the present invention in an embodiment,during thermocompression bonding, a top region of an electric componentis pressed against a wiring board with a predetermined pressure, while aside region of the electric component is pressed with a pressure smallerthan the pressure applied to the top region. Thus, a sufficient pressurecan be applied to a portion at which the electric component and thewiring board are connected to each other, and a fillet portion aroundthe electric component can be pressurized without generating a void.Therefore, it is possible to connect an IC chip or the like with highreliability by using an anisotropic conductive adhesive film, forexample.

According to an embodiment of the present invention, during thethermocompression bonding, an electric component is heated at apredetermined temperature, and a wiring board is heated at a temperaturehigher than the predetermined temperature by means of a heater that isprovided in a supporting base, for example. In this manner, it ispossible to sufficiently heat the fillet portion around the electriccomponent. Therefore, generation of a void can be further prevented.

Moreover, according to an embodiment of the present invention, it ispossible to easily apply pressures to the top region and the side regionof the electric component with a predetermined pressure differencemaintained between those pressures by pressing the compression bondingportion formed of a predetermined elastomer against the top and the sideof the electric component.

In addition, when an elastomer having rubber hardness of 40 or more and80 or less is used for the compression bonding portion, it is possibleto apply optimum pressures to the top region and the side region of theelectric component. Moreover, when the adhesive is heated during thethermocompression bonding so as to achieve melting viscosity of 1.0×10²mPa·s or more and 1.0×10⁵ mPa·s or less, it is possible to remove abinding resin from the connecting portion and prevent generation of avoid during the thermocompression bonding more surely. Therefore,connection with higher reliability can be achieved.

According to an embodiment of the present invention, a mounting deviceincludes a thermocompression bonding head having a compression bondingportion formed of an elastomer having rubber hardness of 40 or more and80 or less and is arranged to press the compression bonding portionagainst an electric component placed on a wiring board with apredetermined pressure. Therefore, the mounting device that can performhighly reliable connection and has a simple configuration can beobtained.

In the present invention in an embodiment, in the case where thethickness of the compression bonding portion of the thermocompressionbonding head is equal to or larger than that of the electric componentor in the case where the size of the compression bonding portion of thethermocompression bonding head is larger than that of the electriccomponent, it is possible to apply optimum pressures to a top region anda side region of the electric component more surely.

Moreover, in the present invention in an embodiment, in the case wherethe size of the compression bonding portion of the thermocompressionbonding head is larger than an area of a region where a plurality ofelectric components are arranged, it is possible to connect thoseelectric components with high reliability at the same time. Therefore,mounting efficiency can be largely improved.

According to the present invention in an embodiment, it is possible tomount an electric component with high reliability by using adhesive.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram showing the configuration of a main partof an embodiment of a mounting device and a thermocompression bondingprocess according to the present invention.

FIG. 2 is a schematic diagram showing the configuration of a main partof an embodiment of a mounting device and a thermocompression bondingprocess according to the present invention.

FIG. 3 is a schematic diagram showing the configuration of anotherembodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of a method and a device for mounting an electric componentaccording to the present invention are now described with reference tothe drawings.

FIGS. 1 and 2 generally show a main part of a mounting device and athermocompression bonding process in the present embodiment.

As shown in FIG. 1, the mounting device 1 of the present embodimentincludes a base 2 on which a wiring board 10 with a wiring pattern 10 aformed thereon is placed and a thermocompression bonding head 4 forpressing and heating an IC chip (electric component) 20 provided with aprotrusion 20 a.

The base 2 is formed of a predetermined metal. A heater 3 is providedinside the base 2.

The thermocompression bonding head 4 has a head body 5 formed of apredetermined metal and a heater (not shown) provided therein.

A concave portion 5 a is formed in a portion of the head body 5 that isopposed to the base 2. A compression bonding portion 6 formed of anelastomer in the form of a plate is attached to the concave portion 5 aso as to be in close contact with the concave portion 5 a.

The compression bonding portion 6 of the present embodiment is arrangedin such a manner that its compression bonding face 6 a is arrangedhorizontally. The compression bonding face 6 a of the compressionbonding portion 6 is formed to have a larger area than a top 20 b of theIC chip 20.

The compression bonding portion 6 has a thickness that is equal to orlarger than that of the IC chip 20.

In the present invention in an embodiment, the type of the elastomerforming the compression bonding portion 6 is not specifically limited.However, it is preferable to use an elastomer having rubber hardness of40 or more and 80 or less from a viewpoint of improving connectionreliability.

An elastomer having rubber hardness that is less than 40 has adisadvantage that a pressure applied to the IC chip 20 is insufficientand initial conduction resistance and connection reliability are notgood. Moreover, an elastomer having rubber hardness that is larger than80 has a disadvantage that a pressure applied to a fillet portion isinsufficient and a void is generated in a binding resin of adhesive,thus lowering connection reliability.

As described herein, a standard conforming to JIS S 6050 is applied torubber hardness.

It is preferable to use any of natural rubber and synthetic rubber asthe above elastomer. From a viewpoint of heat resistance and pressureresistance, silicone rubber is preferably used.

In order to mount the IC chip 20 in the present embodiment having theaforementioned configuration, the wiring board 10 is arranged on thebase 2 and an anisotropic conductive adhesive film 7 is placed on thewiring board 10, as shown in FIG. 1.

The anisotropic conductive adhesive film 7 includes a binding resin 7 aand conductive particles 7 b dispersed in the binding resin 7 a.

Melting viscosity of the binding resin 7 a as adhesive of the presentinvention is not affected by whether or not the conductive particles 7 bare dispersed in the binding resin 7 a, if the amount of the conductiveparticles 7 b in the binding resin 7 a is small.

The IC chip 20 is placed on the above anisotropic conductive adhesivefilm 7. Then, the compression bonding face 6 a of the thermocompressionbonding head 4 is pressed against the top 20 b of the IC chip 20 via aprotection film (not shown) so as to perform preliminary compressionbonding under a predetermined condition. Main compression bonding isthen performed under the following condition.

In the present invention in an embodiment, during the main compressionbonding, the IC chip 20 is heated at a predetermined temperature and thewiring board 10 is heated at a temperature higher than the predeterminedtemperature.

More specifically, the heater of the thermocompression bonding head 4 iscontrolled so as to adjust a temperature of the compression bondingportion 6 to about 100° C. and the heater 3 of the base 2 is controlledto adjust a temperature of the binding resin 7 a of the anisotropicconductive adhesive film 7 to about 200° C. which is the temperature ofthe compression bonding portion 6.

In this manner, the anisotropic conductive adhesive film 7 is heated toachieve melting viscosity of 1.0×10² mPa·s or more and 1.0×10⁵ mPa·s orless during the thermocompression bonding.

In the case where the melting viscosity of the anisotropic conductiveadhesive film 7 is less than 1.0×10² mPa·s during thermocompressionbonding, there is a disadvantage that fluidity of the binding resin 7 aduring the thermocompression bonding is large and a void is generated.Thus, initial conduction resistance and connection reliability are notgood. In the case where the melting viscosity of the anisotropicconductive adhesive film 7 is larger than 1.0×10⁵ mPa·s, the bindingresin 7 a cannot be completely removed from a connecting portion duringthe thermocompression bonding and a void is generated. Therefore,initial conduction resistance and connection reliability are not good.

During the main compression bonding, a pressure of about 100 N isapplied for each IC chip for about 15 seconds.

As shown in FIG. 2, in the present embodiment, pressurization isperformed by means of the compression bonding portion 6 formed of anelastomer having rubber hardness of 40 or more and 80 or less, therebypressing the top 20 b of the IC chip 20 against the wiring board 10 witha predetermined pressure and pressing the fillet portion 7 c at the sideof the IC chip 20 with a pressure smaller than that applied to the top20 b. Thus, it is possible to apply a sufficient pressure to theconnecting portion at which the IC chip 20 and the wiring board 10 areconnected to each other. It is also possible to apply a pressure to thefillet portion 7 c around the IC chip 20 without generating a void.

As a result, it is possible to connect the IC chip 20 or the like withhigh reliability by using the anisotropic conductive adhesive film 7according to the present embodiment.

During the thermocompression bonding, the IC chip 20 is heated at apredetermined temperature and the wiring board 10 is heated at atemperature higher than the predetermined temperature. In this manner,the fillet portion 7 c around the IC chip 20 can be sufficiently heatedand generation of a void can be surely prevented.

Moreover, the anisotropic conductive adhesive film 7 is heated so as toachieve melting viscosity of 1.0×10² mPa·s or more and 1.0×10⁵ mPa·s orless during the thermocompression bonding. Thus, it is possible toremove the binding resin 7 a from the connecting portion and preventgeneration of a void during the thermocompression bonding more surely.Therefore, connection with higher reliability can be performed.

In addition, according to the mounting device 1 of the presentembodiment, a mounting device having a simple configuration that canperform highly reliable connection can be obtained.

Especially, according to the present embodiment, the thickness of thecompression bonding portion 6 is equal to or larger than that of the ICchip 20. Thus, it is possible to surely apply optimum pressures to thetop 20 b of the IC chip 20 and the fillet portion 7 c at the side of theIC chip 20, respectively.

FIG. 3 is a schematic view showing the configuration according toanother embodiment of the present invention. Parts corresponding tothose in the above embodiment are labeled with the same referencenumerals and the detailed description thereof is omitted.

As shown in FIG. 3, a mounting device 1A of the present embodiment isdifferent from that of the above embodiment in that a size of thecompression bonding portion 6 is set to be larger than an area of aregion where a plurality of (e.g., two) IC chips 20 and 21 havingdifferent sizes from each other, for example, are arranged.

In this case, the rubber hardness of the compression bonding portion 6is 40 or more and 80 or less, that is, is the same as that in the aboveembodiment.

According to the present embodiment having the above configuration, itis possible to simultaneously perform connection of a plurality of ICchips 20 and 21 with high reliability, especially in the case where theIC chips 20 and 21 are different from each other in thickness. Thus,mounting efficiency can be largely improved. Except for the above, theconfiguration, operation, and effects of the present embodiment are thesame as those of the above embodiment. Therefore, the detaileddescription of the configuration, operation, and effects of the presentembodiment is omitted.

The present invention is not limited to the aforementioned embodimentsbut can be modified in various ways.

For example, a case is described in the aforementioned embodiments, inwhich the IC chip is mounted by using the anisotropic conductiveadhesive film. However, the present invention is not limited thereto.Alternatively, an adhesive containing no conductive particle may beused.

Moreover, a case is described in the aforementioned embodiments, inwhich the IC chip including a bump electrode is mounted. However, thepresent invention can also be applied to an IC chip having no bumpelectrode.

EXAMPLES

Examples illustrative of the present invention are now described indetail, together with Comparative Examples.

Example 1

A rigid substrate fabricated by forming a Cu pattern having a width of75 μm and a pitch of 150 μm on a glass epoxy substrate and formingnickel/gold plating on that substrate was used as a wiring board. A chiphaving a size of 6×6 mm and a thickness of 0.4 mm, in which bumpelectrodes were formed at a pitch of 150 μm, was prepared as an IC chip.

The IC chip was bonded onto the wiring board by thermocompressionbonding by using a thermocompression bonding head provided with acompression bonding portion which had a size of 60×60 mm and a thicknessof 10 mm and was formed of silicon rubber having rubber hardness of 40.As an anisotropic conductive adhesive film, a film formed by dispersingconductive particles in a binding resin having melting viscosity of1.0×10⁵ mPa·s was used.

In this case, pressurization and heating were performed with a pressureof 100 N/IC (278 N/cm²) for 15 seconds, while a temperature of a basewas controlled to adjust a temperature of the compression bondingportion to 100° C. and a temperature of the anisotropic conductiveadhesive film to 200° C.

Example 2>

Except that the compression bonding portion formed of silicone rubberhaving rubber hardness of 80 was used, thermocompression bonding wasperformed under the same condition as that in Example 1.

Comparative Example 1>

Except that the compression bonding portion formed of silicone rubberhaving rubber hardness of 10 or less was used, thermocompression bondingwas performed under the same condition as that in Example 1.

Comparative Example 2>

Except that the compression bonding portion formed of silicone rubberhaving rubber hardness of 120 was used, thermocompression bonding wasperformed under the same condition as that in Example 1.

Example 3>

Except that an anisotropic conductive adhesive film in which conductiveparticles were dispersed in a binding resin having melting viscosity of1.0×10² mPa·s was used, thermocompression bonding was performed underthe same condition as that in Example 1.

Comparative Example 3>

Except that an anisotropic conductive adhesive film in which conductiveparticles were dispersed in a binding resin having melting viscosity of5 mPa·s was used, thermocompression bonding was performed under the samecondition as that in Example 1.

Comparative Example 4>

Except that an anisotropic conductive adhesive film in which conductiveparticles were dispersed in a binding resin having melting viscosity of1.0×10⁹ mPa·s was used, thermocompression bonding was performed underthe same condition as that in Example 1.

Comparative Example 5>

Except that the compression bonding portion formed of silicone rubber tohave thickness (here, 0.2 mm) thinner than the IC chip was used,thermocompression bonding was performed under the same condition as thatin Example 1.

Reliability Evaluation

Reliability depending on the rubber hardness of the compression bondingportion and that depending on the melting viscosity of the binding resinwere evaluated for the above Examples and Comparative Examples. Tables 1and 2 show the results.

[Table 1] TABLE 1 Evaluation of reliability depending on rubber hardnessof compression bonding portion Comparative Comparative Example 1 Example1 Example 2 Example 2 Rubber hardness 10 or less 40 80 120 Void NoneNone None Generated Initial conduction X ◯ ◯ ◯ resistance Connection X ◯◯ X reliability(Note)Melting viscosity of resin = 1.0 × 10⁵ mPa · S

[Table 2] TABLE 2 Evaluation of reliability depending on meltingviscosity of binding resin Comparative Comparative Example 3 Example 3Example 1 Example 4 Melting Viscosity 5 1.0 × 10² 1.0 × 10⁵ 1.0 × 10⁹ ofresin (mPa · S) Void None None None Generated Initial conduction X ◯ ◯ ◯resistance Connection X ◯ ◯ X reliability(Note)Rubber hardness = 40

For the initial conduction resistance, a resistance value betweenpatterns was measured by four-terminal method. An example or comparativeexample for which the measured resistance value was less than 1 Ω wasrepresented with ∘. An example or comparative example for which themeasured resistance value was 1 Ωor more was represented with x.

For the connection reliability, a resistance value was measured andevaluated, after aging was performed at a temperature of 85° C. and arelative humidity of 85% for 24 hours and then a reflow process having apredetermined profile was performed as follows: temperature increase ata rate of 1° C./S to 4° C./S→after heat at a temperature of 150° C.±10°C. for 30 s±1 s→temperature increase at a rate of 1° C./S to 4°C./S→soldering at a peak temperature of 235° C.±5° C. for 10 s+1s→cooling at a rate of 1° C./S to 4° C./S. An example or comparativeexample for which the measured resistance value was less than 1 Ω wasrepresented with ∘, while an example or comparative example for whichthe measured resistance value was 1 Ω or more was represented with x.

Generation of a void was evaluated with an ultrasonic microscope. Anexample or comparative example for which no void was generated wasrepresented with ∘, while an example or comparative example for which avoid was generated was represented with x.

As shown in Table 1, Example 1 in which the rubber hardness of thecompression bonding portion was 40 and Example 2 in which the rubberhardness of the compression bonding portion was 80 were good in both theinitial conduction resistance and the connection reliability. No voidwas generated in Examples 1 and 2.

On the other hand, in Comparative Example 1 in which the rubber hardnessof the compression bonding portion was less than 40, a pressure appliedto the IC chip was insufficient and therefore the initial conductionresistance and the connection reliability were not good. In ComparativeExample 2 in which the rubber hardness of the compression bondingportion was more than 80, the pressure applied to the fillet portion wasinsufficient, a void was generated in the binding resin of the adhesive,and the connection reliability was not good.

In Example 3 in which the melting viscosity of the binding resin of theanisotropic conductive adhesive film was 1.0×10² mPa·s and Example 1 inwhich the melting viscosity of the binding resin of the anisotropicconductive adhesive film was 1.0×10⁵ mPa·s, both the initial conductionresistance and the connection reliability were good and no void wasgenerated.

On the other hand, in Comparative Example 3 which used the binding resinhaving the melting viscosity less than 1.0×10² mPa·s, the binding resinhad large fluidity during thermocompression bonding and a void wasgenerated. Thus, the initial conduction resistance and the connectionreliability were not good. In Comparative Example 4 which used thebinding resin having the melting viscosity larger than 1.0×10⁵ mPa·s,the binding resin could not be completely removed from the connectingportion during thermocompression bonding and a void was generated. Thus,the initial conduction resistance and the connection reliability werenot good.

Moreover, in Comparative Example 5 which used the compression bondingportion that was thinner than the IC chip, no pressure was applied tothe fillet portion and a void was generated. Thus, the initialconduction resistance and the connection reliability were not good.

The present invention can be applied in any suitable manner. Forexample, the present invention can be used in an application in which anelectric and electronic component such as a semiconductor chip ismounted onto a printed wiring board so as to fabricate a circuit boardduring manufacturing of compact electronic equipment.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A method for mounting an electronic component on a wiring board,comprising thermocompression bonding an electric component onto a wiringboard by using an adhesive, wherein during the thermocompressionbonding, a top region of the electric component is pressed against thewiring board with a predetermined pressure, and a side region of theelectric component is pressed with a side region pressure smaller thanthe pressure applied to the top region.
 2. The method for mounting anelectronic component according to claim 1, wherein the electriccomponent is heated at a predetermined temperature and the wiring boardis heated at a temperature higher than the predetermined temperatureduring the thermocompression bonding.
 3. The method for mounting anelectronic component according to claim 1, wherein a compression bondingportion formed of a predetermined elastomer is pressed against at leasta portion of the top and side regions of the electric component.
 4. Themethod for mounting an electronic component according to claim 3,wherein the predetermined elastomer includes an elastomer having rubberhardness that ranges from about 40 to about
 80. 5. The method formounting an electronic component according to claim 1, wherein theadhesive is heated to achieve a melting viscosity that ranges from about1.0×10² mPa·s to about 1.0×10⁵ mPa·s during the thermocompressionbonding.
 6. The method for mounting an electronic component according toclaim 1, wherein an anisotropic conductive adhesive film in whichconductive particles are dispersed in a binding resin is used as theadhesive.
 7. The method for mounting an electronic component accordingto claim 1, wherein the top region and the side region of the electriccomponent are simultaneously pressed.
 8. A mounting device for mountingan electric component on a wiring board, the mounting device comprisinga thermocompression bonding head having a compression bonding portionformed of an elastomer having rubber hardness that ranges from about 40to about 80, wherein the compression bonding portion is pressed againstan electric component placed on a wiring board with a predeterminedpressure.
 9. The mounting device according to claim 8, wherein athickness of the compression bonding portion of the thermocompressionbonding head is equal to or larger than a thickness of the electriccomponent.
 10. The mounting device according to claim 8, wherein a sizeof the compression bonding portion of the thermocompression bonding headis larger than an area of the electric component placed on the wiringboard.
 11. The mounting device according to claim 8, wherein a size ofthe compression bonding portion of the thermocompression bonding head islarger than an area of a region where a plurality of electric componentsare arranged.
 12. The mounting device according to claim 8, furthercomprising a base for supporting the wiring board, wherein the baseincludes a heater.